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EFFECTS OF 9-WK HINDLIMB SUSPENSION ON FIBER CHARACTERISTICS IN RAT SOLEUS MUSCLE.  T. Nomura^1,2, F. Kawano², T. Wakatsuki², and Y. Ohira².  ¹Res. Ctr. Health Phys. Fit. Sports, Nagoya Univ., Nagoya and ²Sch. Health Sport Sci., Osaka Univ., Osaka, Japan.

     Effects of 9-wk hindlimb suspension (HS) and 8-wk recovery on soleus muscle fiber characteristics were studied in adult rats.  Forty-five male Wistar rats (7-wk old) were divided into three groups: 1) pre-suspension control (n=5); 2) cage-control (n=20); and 3) 9-wk HS (n=20).  Even though the rats were hindlimb-suspended, they were able to eat food and drink water freely by using their forelimbs.  The percent distribution of each type of fibers, cross-sectional area (CSA), quantitative activities of α-glycerophosphate dehydrogenase (α-GPD) and succinate dehydrogenase (SDH) were determined in soleus muscle fibers histochemically.  The growth-related gain of body weight was slightly inhibited by suspension.  Although body weight was gradually increased during recovery, it was still less than controls after 8 wk.  The growth of soleus, however, was completely inhibited by hindlimb suspension, although atrophy, relative to the pre-suspension level, was not induced.  The relative weight of soleus to body weight at the end of suspension period was also lower than that in the pre-suspension control.  The growth-related gains of muscle fiber CSA, as well as fiber transformation toward slow type, were completely inhibited by HS.  No significant changes were observed in the specific activities of α-GPD and SDH of any types of fibers between HS and control groups.  But the total activities of α-GPD and SDH in whole CSA were significantly decreased following HS.  These results suggested that 9-wk HS inhibited both fiber transformation toward slow type and growth of CSA.  Further, the HS-related inhibition of the growth of soleus muscle was not recovered completely after 8-wk ambulation.